Move cabi_realloc to a wit-bindgen-rt crate (bytecodealliance#876)

* Move `cabi_realloc` to a `wit-bindgen-rt` crate

This commit extracts out a `wit-bindgen-rt` crate which unconditionally
provides the `cabi_realloc` function. This'll exist for `cargo
component` to add a dependency on and otherwise the `wit-bindgen` crate
isn't actually need at runtime at all.

* Remove realloc feature gate

* Add runtime to publish script

* Remove realloc feature guard in build script

Author: alexcrichton

.github/workflows/main.yml

@@ -137,6 +137,12 @@ jobs:
     - run: cargo build --no-default-features --features csharp
     - run: cargo build --no-default-features --features markdown
 
+    # Feature combos of the `wit-bindgen` crate
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features --features realloc
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features --features macros
+    - run: cargo build --target wasm32-wasi -p wit-bindgen --no-default-features --features macros,realloc
+
     # Verity that documentation can be generated for the rust bindings crate.
     - run: cargo doc -p wit-bindgen --no-deps
       env:

Cargo.lock

@@ -25,6 +25,7 @@ const CRATES_TO_PUBLISH: &[&str] = &[
     "wit-bindgen-teavm-java",
     "wit-bindgen-markdown",
     "wit-bindgen-rust-macro",
+    "wit-bindgen-rt",
     "wit-bindgen",
     "wit-bindgen-cli",
 ];

ci/publish.rs

@@ -43,7 +43,7 @@ version=$(grep '^version =' ./Cargo.toml | sed 's/.*"\(.*\)"/\1/' | sed 's/\./_/
 
 sym=cabi_realloc_wit_bindgen_$version
 
-cat >./crates/guest-rust/src/cabi_realloc.rs <<-EOF
+cat >./crates/guest-rust/rt/src/cabi_realloc.rs <<-EOF
 // This file is generated by $0
 
 #[no_mangle]
@@ -53,11 +53,11 @@ pub unsafe extern "C" fn $sym(
     align: usize,
     new_len: usize,
 ) -> *mut u8 {
-    crate::rt::cabi_realloc(old_ptr, old_len, align, new_len)
+    crate::cabi_realloc(old_ptr, old_len, align, new_len)
 }
 EOF
 
-cat >./crates/guest-rust/src/cabi_realloc.c <<-EOF
+cat >./crates/guest-rust/rt/src/cabi_realloc.c <<-EOF
 // This file is generated by $0
 
 #include <stdint.h>
@@ -70,16 +70,16 @@ void *cabi_realloc(void *ptr, size_t old_size, size_t align, size_t new_size) {
 }
 EOF
 
-rm -f crates/guest-rust/src/cabi_realloc.o
-$WASI_SDK_PATH/bin/clang crates/guest-rust/src/cabi_realloc.c \
-  -O -c -o crates/guest-rust/src/cabi_realloc.o
+rm -f crates/guest-rust/rt/src/cabi_realloc.o
+$WASI_SDK_PATH/bin/clang crates/guest-rust/rt/src/cabi_realloc.c \
+  -O -c -o crates/guest-rust/rt/src/cabi_realloc.o
 
 # Remove the `producers` section. This appears to differ whether the host for
 # clang is either macOS or Linux. Not needed here anyway, so discard it to help
 # either host produce the same object.
-wasm-tools strip -d producers ./crates/guest-rust/src/cabi_realloc.o \
-  -o ./crates/guest-rust/src/cabi_realloc.o
+wasm-tools strip -d producers ./crates/guest-rust/rt/src/cabi_realloc.o \
+  -o ./crates/guest-rust/rt/src/cabi_realloc.o
 
-rm -f crates/guest-rust/src/libwit_bindgen_cabi_realloc.a
-$WASI_SDK_PATH/bin/llvm-ar crus crates/guest-rust/src/libwit_bindgen_cabi_realloc.a \
-  crates/guest-rust/src/cabi_realloc.o
+rm -f crates/guest-rust/rt/src/libwit_bindgen_cabi_realloc.a
+$WASI_SDK_PATH/bin/llvm-ar crus crates/guest-rust/rt/src/libwit_bindgen_cabi_realloc.a \
+  crates/guest-rust/rt/src/cabi_realloc.o

ci/rebuild-libcabi-realloc.sh

@@ -12,10 +12,11 @@ Used when compiling Rust programs to the component model.
 """
 
 [dependencies]
-wit-bindgen-rust-macro = { path = "../rust-macro", optional = true, version = "0.20.0" }
+wit-bindgen-rust-macro = { path = "./macro", optional = true, version = "0.20.0" }
+wit-bindgen-rt = { path = "./rt", optional = true, version = "0.20.0" }
 bitflags = { workspace = true }
 
 [features]
 default = ["macros", "realloc"]
-macros = ["wit-bindgen-rust-macro"]
-realloc = []
+macros = ["dep:wit-bindgen-rust-macro"]
+realloc = ["dep:wit-bindgen-rt"]

crates/guest-rust/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "wit-bindgen-rt"
+version.workspace = true
+edition.workspace = true
+repository = 'https://github.com/bytecodealliance/wit-bindgen'
+license = "Apache-2.0 WITH LLVM-exception"
+homepage = 'https://github.com/bytecodealliance/wit-bindgen'
+description = """
+Runtime support for the `wit-bindgen` crate
+"""

crates/rust-macro/Cargo.toml renamed to crates/guest-rust/macro/Cargo.toml

@@ -1,8 +1,4 @@
 fn main() {
-    if !cfg!(feature = "realloc") {
-        return;
-    }
-
     let target_arch = std::env::var("CARGO_CFG_TARGET_ARCH").unwrap_or(String::new());
     let target_family = std::env::var("CARGO_CFG_TARGET_FAMILY").unwrap_or(String::new());